This invention relates to a method and an apparatus for writing an oxide film.
In the field of vapor-phase growth, attention has been recently focused on a photo CVD (chemical vapor deposition) method which uses luminous energy to excite or activate gases. The photo CVD is generally better than conventional thermal CVD or plasma CVD in temperature characteristics and damaging characteristics. If a laser is used as a light source, the photo CVD enables direct writing of a film.
During the production of a film by a photo CVD method, atoms of gases of materials for the film absorb energy of applied light and are thereby activated. The activation of gas atoms advances the formation of the film. Accordingly, the selection of a light source and material gases is important in the photo CVD method.
In respect of photo CVD methods, oxide films of SiO.sub.2 have been widely studied. Most of such SiO.sub.2 films are formed by photo CVD methods in which a light source is a lamp generating light with a wavelength equal to or shorter than 200 nm; a gas source includes SiH.sub.4 or Si.sub.2 H.sub.6 ; and an oxidizing gas is O.sub.2. The reason for the use of such a light source is that SiH.sub.4 gas absorbs light with a wavelength equal to or shorter than 160 nm and Si.sub.2 H.sub.6 gas and O.sub.2 gas absorb light with a wavelength equal to or shorter than 200 nm. In some cases, the lamp of the light source is replaced by an excimer laser. All of known photo CVD methods related to SiO.sub.2 films are intended to merely form a two-dimensional film and are incapable of directly writing a film.
Japanese Journal of Applied Physics, Vol 126, No. 3, PPL 186, relates to a photo CVD method of forming a film of SnO.sub.2. In this photo CVD method, a light source is composed of a mercury lamp emitting light with wavelengths of 185 nm and 254, and an O.sub.2 gas and a tin compound gas are used as gas sources. The photolysis of O.sub.2 molecules by the 185-nm light triggers a reaction forming the SnO.sub.2 film.
The inventors of this application and others achieved directly writing of an SnO.sub.2 film on a glass substrate by a method in which a CO.sub.2 laser is used to locally heat a surface of the substrate. In this method, the heat caused a significant damage to the substrate and the material for the substrate is considerably limited.
Light CVD methods using lasers are referred to as laser CVD methods. The laser CVD methods feature that the density of luminous energy is high and the beam of light is coherent and directive. Accordingly, it seems possible for a laser CVD method to quicky form a localized film through a film-directly-writing process.
In the field of metal materials, directly writing methods by laser CVD have been studied in revising wiring patterns or mask patterns.